Figures and data in A small number of workers with specific personality traits perform tool use in ants

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5 figures, 6 tables and 7 additional files

Figures

Figure 1

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Procedure followed in experiment 2.

Each sub-colony received honey and tools in steps 1 and 3. The yellow items represent the tools (small pieces of sponge,~1 mm3), below is shown the plate with diluted honey (0.25 ml). In step 2, the ants received five cricket legs (*Acheta domestica*). On day 5, the ants received 20 tools and the honey bait (A). For individual workers that transported four consecutive tools to the bait, the time needed to transport one tool significantly decreased within one trial (B). For individual workers that transported at least two consecutive tools in different trials, the time needed to transport one tool to the bait did not change among trials (C). Box plots show medians, quartiles, min-max values, outliers (black dots) and individual data points (empty circles). NS – non-significant, *: p<0.05, ****: p<0.0001.

Figure 1—source data 1 Experiment 2 - the time (sec) needed to transport one tool by the same individual that performed consecutive tool transports to the bait within a single trial. The time required for the transport of each tool during consecutive transports by the same worker within a trail was analysed with LMM (Gaussian error, maximum likelihood fit). Only workers that performed four consecutive transports were included in the analysis (N = 54; second-third tool: p=0.03, second-fourth tool: p<0.001).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig1-data1-v1.xlsx
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Figure 1—source data 2 Experiment 2 - the time (sec) needed to transport one tool for individual workers that transported at least two consecutive tools in different trials. The average time needed to transport one tool by the same worker between the trials was analysed with LMM (Gaussian error, maximum likelihood fit). Up to three trials were included (N = 29; first-second trial: p=0.99; first-third trials: p=0.32).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig1-data2-v1.xlsx
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Figure 2

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Effect of the pre-trial in experiment 2.

There was no significant difference between the different groups of sub-colonies in the latency to transport the first tool to the bait (A) and the total time needed to transport the 10 tools to the bait (B). Sub-colonies 2: had a pre-trial (liquid food and tools simultaneously); Sub-colonies 1: without a pre-trial (received first food and then tools in absence of the food). Workers manipulating tools during the pre-trial were removed (see Materials and methods). Box plots show median, quartiles, min-max values and outliers (black dot).

Figure 2—source data 1 Experiment 2 - the latency (sec) to transport the first tool to the bait by the two subcolonies with and without a pre-trial. The effect of the pre-trial on the latency to bring the first tool to the bait in the first trial was analysed with LMM (Gaussian error, maximum likelihood fit). All colonies (N = 6) and subcolonies (N = 12) were included (p=0.64).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig2-data1-v1.xlsx
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Figure 2—source data 2 Experiment 2 - the total time (sec) needed to transport the ten tools to the bait by the two subcolonies with and without a pre-trial. The effect of the pre-trial on the total transport time observed during the subsequent first trial was analysed with LMM (Gaussian error, maximum likelihood fit). All colonies (N = 6) and subcolonies (N = 12) were included (p=0.42).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig2-data2-v1.xlsx
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Figure 3

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Experimental set-up used for the open-field (A) and the reaction to prey tests (B).

The ant is in the acclimatisation tube for 1 min and the test starts when the tube is removed (see Materials and methods). The consistency across the two sessions of the open-field test regarding the time spent in the central area (C) and the consistency across the two sessions of the reaction to prey test (D). The black line with confidence band (grey) is plotted based on the Pearson correlation of the two variables.

Figure 3—source data 1 Experiment 3 - correlation between the two sessions (repeats) for the time (sec) spent walking in the central area (open-field test) by individual ants. Repeatability across the two sessions, for each individual ant, concerning the time spent walking in the central area was assessed with intra-class correlation (Lessells and Boag, 1987) by using LMM (Nakagawa and Schielzeth, 2010). The total time spent in the central area were significantly repeatable across the two sessions (N = 154; p<0.0001). Six ants died between the two sessions of the personality tests, therefore the sample size is 154 ants instead of 160 (20 ants in each of the eight sub-colonies).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig3-data1-v1.xlsx
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Figure 3—source data 2 Experiment 3 - correlation between the two sessions (repeats) for the time (sec) spent in contact with the prey (reaction to prey test). Repeatability across the two sessions, for each individual ant, concerning the time spent in contact with the prey was assessed with intra-class correlation (Lessells and Boag, 1987) by using LMM (Nakagawa and Schielzeth, 2010). The time spent in contact with the prey was highly repeatable (N = 154; p<0.0001). Six ants died between the two sessions of the personality tests, therefore the sample size is 154 ants instead of 160 (20 ants in each of the eight sub-colonies).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig3-data2-v1.xlsx
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Figure 4

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Procedure followed in experiment 3.

Test-sub-colonies received honey and tools in every trial. The yellow items represent the tools (small pieces of sponge,~1 mm³), below is shown the plate with diluted honey (0.25 ml). On days 1–3, two trials were performed (10 tools offered), and after each trial, the ants that transported tools to the bait were removed. On day 4, one trial (10 tools offered) was performed and then the previously removed workers were returned to their test-sub-colony. All the workers were used in Trial 8, in which 20 tools were offered.

Figure 5

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Plots of the first two dimensions of the Principal Component Analysis.

Correlation circle of the variables: TWalk.Out (time spent walking in the periphery), TotT.Center (total time spent in the central area); TContact.Prey (time in contact with the prey) (A). Projection of individuals on the PCA factorial space: red dots refer to ants that used tools, black dots refer to ants that did not use tools; the confidence ellipses representing individuals using tools (red arrow) or not (green arrow) show significant difference (no overlap) (B). The probability of using tools is linked to the individual personality score. The mean and CI of the personality score and the individual data points (empty circles) for the non-tool users (mean = −0.33, CI [−0.56,–0.09]) and tool users (mean = 0.57, CI [0.26, 0.88]) is plotted (C). The ants’ personality score significantly predicted the probability of using tools (***: p<0.001).

Figure 5—source data 1 Experiment 3 - the variables used in the Principal Component Analysis. A ‘personality score’ for each ant was calculated with a Principal Component Analysis based on (a) total time spent in the central area of the open field, (b) time spent walking in the periphery, (c) time spent in contact with the prey (average of the two sessions for each variable). The figures show the average values of the two sessions used to study the behaviours observed in the two personality tests: open-field and reaction to prey (N = 154). Six ants died between the two sessions of the personality tests, therefore the sample size is 154 ants instead of 160 (20 ants in each of the eight sub-colonies).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig5-data1-v1.xlsx
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Figure 5—source data 2 Experiment 3 - the differences in personality score between tool user and non-tool user workers. The personality score of a given ant is represented by its individual value related to the first principal component, accounting for the 59.14% of the total variance, normalised by subtracting the mean value for its colony. The link between personality score and tool use behaviour (tool user or not) was analysed with a GLMM, binomial error structure (logit-link). The ants’ personality score significantly predicted the probability to use tools in at least one trial (N = 154, p<0.001). Six ants died between the two sessions of the personality tests, therefore the sample size is 154 ants instead of 160 (20 ants in each of the eight sub-colonies).: https://cdn.elifesciences.org/articles/61298/elife-61298-fig5-data2-v1.xlsx
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Tables

Table 1

Experiment 1: tool use process in whole colonies.

Summary table showing the number of workers present in the arena (# workers in arena), the latency to drop the first tool on the bait (First tool on bait), the total time devoted to tool transport to the bait (Tot. time tool transport), the number of tools transported to the bait (# tools on bait), the latency to transport the first tool to the nest from the start of the experiment (First tool to nest) and the number of workers involved in tool transport to the bait (# workers transp. tools to bait). Five replicates (R1-R5) for each colony are shown. The last column shows the number of tools transported by each worker to the bait (# tools transp. by each worker); for instance, in R1 there were two tool users, one transported nine tools and the other 1.

Colony	# Workers in arena	First tool on bait (min)	Total time tool transport (min)	# Tools on bait	First tool to nest (min)	# Workers transp. tools to bait	# Tools transp. by each worker
1 R1	19	9	21	10	174	2	9; 1
1 R2	43	19	19	10	-	2	5; 5
1 R3	16	23	15	10	201	3	1; 8; 1
1 R4	23	13	37	9	-	2	7; 2
1 R5	29	4	23	10	-	2	5; 5
2 R1	6	26	22	10	111	5	1; 2; 1; 4; 2
2 R2	14	7	20	10	96	2	2; 8
2 R3	40	1	15	8	-	3	3; 1; 4
2 R4	30	3	25	10	144	2	5; 5
2 R5	71	2	10	10	126	3	7; 2; 1
3 R1	16	45	20	10	-	3	1; 4; 5
3 R2	9	7	6	10	172	2	8; 2
3 R3	23	7	7	10	222	1	10
3 R4	4	18	24	10	178	1	10
3 R5	7	120	31	9	214	2	5; 4

Table 2

Experiment 1: tool use process in whole colonies.

The tool use behaviour is composed of two parts: transport of tools to the food source (bait) and transport of imbibed tools inside the nest. The table shows the total number of tool users that participated (Particip.) in both parts of the tool use process and those that transported tools to the bait (# tool users), tool users that were marked (Marked tool users), number of workers that transported more than one tool within a trial (>1 tool within trial), and that transported more than one tool among trials (>1 tool among trials). Shown is the total for the three experimental colonies (sum of five trials each).

		Transport to bait				Transport to nest
Colony	# particip. in both parts	# Tool users	Marked tool users	>1 tool within same trial	>1 tool across trials	Marked tool users	>1 tool within same trial
1	1	11	5	5	1	3	1
2	1	15	3	3	1	5	1
3	2	9	8	8	0	9	1

Table 3

Experiment 1: tool use process in whole colonies.

The tool users were not the first workers obtaining information about the presence of food and tools. The table shows the number of workers that contacted both the tools and the food before the first tool was dropped into the bait; the latency (Lat.) for the first worker to obtain information (info.) about the presence of both the tools and the food and the latency for the first tool user to obtain information about the tools and the food.

Colony	# Workers contacting tools and food before the first tool was dropped on the bait	Lat. first worker having info. about both tools and food (min)	Lat. first tool user having info. about both tools and food (min)
1 R1	10	2.61	7
1 R2	17	0.17	17
1 R3	11	0.55	23
1 R4	18	0.38	2
1 R5	8	0.7	3
2 R1	5	18.03	25
2 R2	5	0.98	7
2 R3	3	0.75	1
2 R4	4	0.87	2
2 R5	5	0.18	1
3 R1	27	0.75	45
3 R2	4	1.92	7
3 R3	11	1.05	7
3 R4	4	1.85	5
3 R5	33	1.75	106

Table 4

Experiment 2: Is there specialisation in tool use?

The total number of tool users and cricket leg transporters (transp.) and the percentage of workers that performed repeated tool use within or between trials or that participated also in the transport of cricket legs. The last column shows the number of very active workers, which participated in at least two tool use trials and one leg transport.

Colony/ subcolony	Total tool users	Repeats within (%)	Repeats between (%)	Transporting also legs (%)	Total leg transp.	% tool users among leg transp.	≥2 trials, ≥1 leg (%)
1/1	6	4 (66.7)	1 (16.7)	2 (33.3)	6	33.3	1 (16.7)
1/2	4	3 (75)	1 (25)	1 (25)	5	20	1 (25)
2/1	12	7 (58.3)	2 (16.7)	1 (8.3)	1	100	-
2/2	10	8 (80)	4 (40)	2 (20)	5	40	2 (20)
3/1	6	6 (100)	5 (83.3)	1 (16.7)	7	14.3	1 (16.7)
3/2	12	8 (66.7)	3 (25)	3 (25)	3	100	2 (16.7)
4/1	8	5 (62.5)	2 (25)	3 (37.5)	6	50	1 (12.5)
4/2	10	7 (70)	4 (40)	3 (30)	6	50	2 (20)
5/1	6	3 (50)	3 (50)	2 (33.3)	4	50	2 (33.33)
5/2	5	2 (40)	2 (40)	1 (20)	4	25	-
6/1	14	8 (57.1)	3 (21.4)	4 (28.6)	7	57.1	2 (14.29)
6/2	6	3 (50)	1 (16.7)	2 (33.3)	5	40	1 (16.7)
Average	8.25	5.33 (64.7)	2.58 (33.3)	2.08 (25.9)	4.92	48.31	1.25 (15.15)

Table 5

Experiment 2: is there specialisation in tool use?

Number of workers participating in more than one trial and the average number of tools they transported.

Colony/ subcolony	Two trials	# Tools	Three trials	# Tools	Four trials	# Tools
1/1	1	9.5
1/2					1	3.75
2/1	2	4
2/2	4	3.12
3/1	5	3.3
3/2	2	1.75			1	3.75
4/1			2	3
4/2	4	1.75
5/1	3	3
5/2	2	3.25
6/1	3	1.5
6/2			1	8.33
Average	2.89	3.46	1.50	5.67	1.00	3.75

Table 6

Experiment 2: is there specialisation in tool use?

The total number of workers using tools in the last trial (trial with 20 tools) and the number of workers that performed tool use also in previous trials (10 tools).

Colony/ subcolony	Total # tool users	# Using tools in previous trials (%)
1/1	4	2 (50%)
1/2	4	1 (25%)
2/1	5	3 (60%)
2/2	5	1 (20%)
3/1	4	3 (75%)
3/2	3	2 (66.7%)
4/1	2	1 (50%)
4/2	2	1 (50%)
5/1	-	-
5/2	5	3 (60%)
6/1	5	3 (60%)
6/2	8	3 (37.5%)
Average	4.27	2.09 (50.38%)